Impact-pressure controlled orientation of shatter cone magnetizations in Sierra Madera,Texas, USA     

T. Adachi  G. Kletetschka 《Studia Geophysica et Geodaetica》2008,52(2):237-254

A suite of Sierra Madera Impact deformed rocks was studied and magnetic analyses were performed. We characterized the magnetic signatures of two locations, sites A and B that have different physical characteristics of shock fractured structures as well as the magnetic signatures. Shatter cone at site A has a fine-scale (few to ∼10 mm) distributed array of complete shatter cones with sharp apex. Natural remanent magnetization (NRM) of site A shatter cone is distributed within the plane that is perpendicular to the apexes of the cones. Shatter cone at site B shows no apparent cone shape or apex, instead, a relatively larger scale and multiple striated joint set (MSJS) and sinusoidal continuous peak. NRM of site B shatter cone is clustered along the apexes. The difference in magnetization direction is a likely indicator of the shock pressure where parallel to apex indicates pressures larger than 10 GPa and perpendicular to apex indicate pressures less than 10 GPa. Intensities of NRM and saturation isothermal remanent magnetization (SIRM) contrast and fluctuate within a shatter cone as well as in between two sites. We observed a random orientation of magnetic vector directions and amplitudes changing over small scales leading to the absence of coherent macro-scale signature.  相似文献   

Estimating thermal inflow to El Chichón crater lake using the energy-budget,chemical and isotope balance approaches     

Yuri Taran  Dmitri Rouwet 《Journal of Volcanology and Geothermal Research》2008

El Chichón crater lake appeared immediately after the 1982 catastrophic eruption in a newly formed, 1-km wide, explosive crater. During the first 2 years after the eruption the lake transformed from hot and ultra-acidic caused by dissolution of magmatic gases, to a warm and less acidic lake due to a rapid “magmatic-to-hydrothermal transition” — input of hydrothermal fluids and oxidation of H₂S to sulfate. Chemical composition of the lake water and other thermal fluids discharging in the crater, stable isotope composition (δD and δ¹⁸O) of lake water, gas condensates and thermal waters collected in 1995–2006 were used for the mass-balance calculations (Cl, SO₄ and isotopic composition) of the thermal flux from the crater floor. The calculated fluxes of thermal fluid by different mass-balance approaches become of the same order of magnitude as those derived from the energy-budget model if values of 1.9 and 2 mmol/mol are taken for the catchment coefficient and the average H₂S concentration in the hydrothermal vapors, respectively. The total heat power from the crater is estimated to be between 35 and 60 MW and the CO₂ flux is not higher than 150 t/day or ~ 200 gm^− 2 day^− 1.  相似文献   

Repeating earthquakes recorded by Liaoning Regional Seismograph Network     

李宇彤  吴忠良  蒋长胜  李广平 《地震学报(英文版)》2008,21(4):386-397

In the list of ’repeating pairs’ or ’doublets’ of earthquakes in China identified by Schaff and Richards using tele-seismic waveform cross-correlation, there were 23 repeating pairs located in Liaoning Province. In this study the waveforms of these events were cross-correlated using records from Liaoning Regional Seismograph Network (LRSN), and the ’repeating events’ in the sense of regional waveform cross-correlation were obtained. The result was compared with that of Schaff and Richards and was used for the assessment of the seismic phase picking and event location practice of LRSN. The result shows that ’repeating events’ in the sense of teleseismic waveform cross-correlation and those in the sense of regional waveform cross-correlation have significant difference, al-though with some overlap. However, the overall assessment of the location accuracy and the phase pick errors of LRSN by using these two sets of ’repeating events’, respectively, provides similar results, while ’repeating events’ in the sense of regional waveform cross-correlation seem to be better performing in such an assessment. With the assumption that the separation between the ’repeaters’ be less than 1 km, the uncertainty in routine earthquake location of LRSN is estimated to be below 5 km, with the average of 2 km. In the observational bulletins of LRSN the time error in phase picking is estimated to be within ±1s for 94% Pg readings and for 88% Sg readings.  相似文献   

岫岩5．4级地震前震源参数与地震波异常变化     

张萍  邹向荣  仇小丽 《地震地磁观测与研究》2008,29(2):7-13

通过搜集辽宁地震台网1997～2004年8个台站记录的ML≥2．5地震观测资料,结合前期工作,对岫岩5．4级地震前后地震波特征进行了分析。结果表明：在岫岩5．4级地震前,P波初动、P波和S波振幅比、小震综合节面解及岫岩ML≥4．0地震震源机制解等同时出现明显的变化。  相似文献   

月球撞击坑的动力学研究   总被引：4，自引：0，他引：4       下载免费PDF全文

张新琴  夏秀文 《地球物理学进展》2008,23(6):1797-1801

月球探测和月球资源的合理利用引起了广泛关注,月球撞击坑的研究可以提供月球的重要信息.统计研究表明,撞击坑的直径和大于该直径的撞击坑数目之间满足分形分布N(≥D)∝r-FD,撞击坑的深度和撞击坑的直径满足多项式关系d=kdDn.简化月球表面撞击过程为一个简单的完全非弹性碰撞,可以得到撞击的动力学微分方程;对撞击过程的阻力项做非线性近似并忽略非齐次项,可以得到撞击方程的解析解:y=dtanh(kdt).由此得到撞击物的撞击速率随撞击深度二次方减小:v=kd2-ky2,撞击坑形貌方程满足方程:lnr=1/nln(kd2)/(vt)-β/nr.理论推导撞击坑的深度和撞击坑的直径满足多项式关系,这和实际撞击坑的统计结果相符合.在无标度区域,撞击物的速率和大于该撞击速率的撞击物数目之间满足分形关系:N(≥v)∝v-FD,速率分布为:f(v)∝v-(FD+1).  相似文献   

Dynamic modeling suggests terrace zone asymmetry in the Chicxulub crater is caused by target heterogeneity     

Gareth S. Collins  Joanna Morgan  Penny Barton  Gail L. Christeson  Sean Gulick  Jaime Urrutia  Michael Warner  Kai Wünnemann 《Earth and Planetary Science Letters》2008,270(3-4):221-230

We investigate the cause of terrace zone asymmetry in the Chicxulub impact crater using dynamic models of crater formation. Marine seismic data acquired across the crater show that the geometry of the crater's terrace zone, a series of sedimentary megablocks that slumped into the crater from the crater rim, varies significantly around the offshore half of the crater. The seismic data also reveal that, at the time of impact, both the water depth and sediment thickness varied with azimuth around the impact site. To test whether the observed heterogeneity in the pre-impact target might have affected terrace zone geometry we constructed two end-member models of upper-target structure at Chicxulub, based on the seismic data at different azimuths. One model, representing the northwest sector, had no water layer and a 3-km thick sediment layer; the other model, representing the northeast sector, had a 2-km water layer above a 4-km sediment layer. Numerical models of vertical impacts into these two targets produced final craters that differ substantially in terrace zone geometry, suggesting that the initial water depth and sediment thickness variations affected the structure of the terrace zone at Chicxulub. Moreover, the differences in terrace zone geometry between the two numerical models are consistent with the observed differences in the geometry of the terrace zone at different azimuths around the Chicxulub crater. We conclude that asymmetry in the pre-impact target rocks at Chicxulub is likely to be the primary cause of asymmetry in the terrace zone.  相似文献   

Lake sedimentological and ecological response to hyperthermals: Boltysh impact crater,Ukraine          下载免费PDF全文

Alena Ebinghaus  David W. Jolley  Steven D. Andrews  David B. Kemp 《Sedimentology》2017,64(6):1465-1487

The Boltysh meteorite impact crater, Ukraine, formed at the Cretaceous–Palaeogene boundary at ca 65·2 Ma. A borehole drilled in the central part of the crater cored a >400 m thick high‐resolution lacustrine succession that covers the Dan‐C2 hyperthermal event associated with a negative carbon isotope excursion. Continuous terrestrial records of past hyperthermals are of limited availability, which makes this record a unique case study of the continental impact of rapid climate warming. This study uses high‐resolution sedimentological core log data together with thin‐section, X‐ray diffraction, microprobe and palynological analyses to: (i) reconstruct lake sedimentological and ecological development across the carbon isotope excursion; and (ii) assess the environmental effect of hyperthermals on terrestrial ecosystems. Based on detailed facies analysis, five gradual stages of lake formation are identified, which show a strong relationship to carbon isotope shifts and associated climatic trends. Initially, sediment supply into the Boltysh lake was controlled by crater morphology. During later lake stages, sediment supply was increasingly controlled by changes in inflow–evaporation ratios which affected seasonal stratification patterns and longer term lake levels. An inferred increase in atmospheric pCO₂ related to the carbon isotope excursion, together with increasing mean annual temperatures, was probably responsible for periodic increases in biological activity of photosynthesising organisms and biomass production. These fluctuations in facies and lake settings largely correspond to orbital‐paced moisture availability oscillations. The gradual reduction in sediment supply commencing during early lake formation prior to carbon isotope excursion inception suggest that the Dan‐C2 event did not initiate sedimentary changes, but intensified sedimentary response to orbital controlled climate change.  相似文献   

多孔同段爆破漏斗形成机理的数值模拟研究   总被引：3，自引：0，他引：3  

王鹏  周传波  耿雪峰  贾建红 《岩土力学》2010,31(3):993-997

采用ANSYS/LS-DYNA非线性三维动力有限元软件,对岩石在多孔同段爆破作用下的应力分布与传播机制,进行了数值模拟。得到了不同时刻的应力分布云图和典型单元的应力-时间历程曲线, 根据结果分析研究了应力波传播规律与爆破漏斗的形成过程,探讨了影响爆破漏斗形成的相关因素,并通过现场试验加以验证,试验结果与数值模拟结果相吻合。  相似文献   

南极GRV 99027火星陨石的地球化学特征          下载免费PDF全文

王鹤年  谢志东  徐伟彪  梁英 《极地研究》2009,21(4):105-128

南极GRV 99027陨石是二辉橄榄岩质辉玻无球粒陨石(L-S)的火星陨石,具有嵌晶、非嵌晶和冲击熔融袋结构。矿物模式组成以橄榄石(55%)、辉石(37.5%)为主,有少量熔长石(6%)、铬铁矿(1.5%)以及微量白磷钙石、陨硫铁等。本文在阐述该陨石的岩石学和矿物化学特征的基础上进一步研究了稀土元素及氢同位素的地球化学特征。该陨石∑REE总量低;橄榄石及辉石以HREE富集为特征;熔长石富LREE,且具高正的δEu;副矿物白磷钙矿含量虽少(约0.2%),但具有极高的∑REE,LREE≈HREE,δEu负异常明显。GRV99027全岩稀土元素分配模式与L-S陨石的模式十分相似,而与SNC其它类型陨石的REE分配模式不同,反映不同类型火星陨石物质源区不同。火星陨石氢同位素以高δD为特征,各类含水矿物对陨石δD的贡献不同。陨石磷酸盐矿物中δD-水含量间一般没有正相关性,间或存有弱的负相关性。根据GRV99027陨石的矿物学模式,REE分配模式,及氢同位素特征,可以确定GRV99027陨石为L-S陨石。为了探讨GRV99027陨石的物质源区及演化历史,我们广泛收集了L-S火星陨石的Sr,Nd,Pb,Os和稀有气体同位素...  相似文献   

6块新回收沙漠陨石的矿物岩石学特征及类型划分     

戴德求  杨荣丰  陈新跃 《地学前缘》2014,21(6):92-101

干旱沙漠地区与南极冰盖均有利于陨石样品保存。2013年4-5月,通过首次新疆哈密沙漠陨石考察,回收了陨石样品47块。文中报导其中6块样品的矿物岩石学特征,并划分它们的化学岩石类型。Arlatager004、006、0014、0022和TuzLeik001等5块样品主要由橄榄石、辉石、长石、铁镍金属和陨硫铁组成,具有典型的普通球粒陨石岩石结构特征,其球粒结构不明显,表明经历过较强的热变质,岩石类型划分为5型;根据样品中橄榄石Fa值,低钙辉石Fs值和样品的金属含量等,将Arlatager004、006、0014、0022划分为L5型普通球粒陨石;TuzLeik001划分为H5型普通球粒陨石。Kumtag005具有典型的球粒结构,结合橄榄石Fa值和低钙辉石Fs值以及岩石学特征,将其划分为L3型普通球粒陨石。根据橄榄石Fa值与其百分标准平均方差(PMD)之间的关系,将Kumtag005的岩石类型亚型划分为L 3.4。这6块样品代表了3个化学群,结合该地区回收到的其他陨石分析结果,表明新疆哈密沙漠是一个新的陨石富集区,这些沙漠陨石的发现和研究,必将极大促进中国陨石学和天体化学的发展。  相似文献